People are still bleaching Ploughman notes in an effort to disguise their true condition. So buyer beware out there.
Cleaning reduces the value of notes, and is to be discouraged. Some collectors and dealers would not buy a note that has been cleaned. All respectable dealers and auctioneers mention if a note has been cleaned by listing it as 'Pressed'. Pressed doesn't go anywhere near describing the £1 note below.

Here are two recent examples of banknote cleaning.
Spot the difference!

The £5 note was offered on ebay in May, 2014.
It appeared again in August, 2014, having been treated with some agent to lighten the mould damage. A nasty fate to befall a previously ok note. Note the artificial flatness of the after picture.

Cleaned Ploughman fiver.

An even worse job was done on this £1 note! They likely used too much bleach on the mouldy areas.

Offered in June, 2014, as a low grade, but respectable note.
It surfaced again October, 2014. Not really worth more than face value with this mutilation.

Here's a Lavery £50 note that turned up on ebay in 2009. It reappeared very shortly after being processed.
A pity, as 'Sterling' era fifty Pound notes are scarce. Not scarce enough to be worth much more than face value with this level of cleaning though. One wonders what it was washed with in order to lighten the ink and foxing.

I almost feel sorry for the stupid moron(s) who tried to clean these Ploughman notes, almost. May they suffer financially for their stupidity.
Here's a National Bank £1 Ploughman note that appeared on a well-known online market place recently.

There's a scan of it in the PSS database before it was messed with:
The before pic dates from 13 Sept 2014, the bleached image from 03 Feb 2016.

There is a group of these Ploughman notes, around 15-20 all with mould damage. They turned up in auction in Dublin a few years back. Most are dated 6.5.29, quite a rare date for some of the more common banks. It is an annoying shame that they are being destroyed in this fashion by stupid people.

Here is a good example of a washed banknote. The white mottling on the surface is due to abrasion, with the ink of the note having been worn away to expose the paper. This is clearest on the portrait. The note is also limp, and sometimes the fibres of the paper will have been disturbed and will be loos on the surface.

Here is another example of a heavily cleaned note sold recently on ebay. The original note sold is shown with a large tear and tape mark. The processed note shown below is cleaned and pressed. Amazingly, the tear was not mentioned in the ebay auction description !

Yes, the same seller sold both the Munster & Leinster £5 and the National Bank £5 notes. I agree that the tear would be apparent once the note was available for inspection. However, by that time the note would have been purchased and would need to be returned for a refund.

Here is avery interesting Ploughman note I spotted on ebay recently. It is interesting in that it has been washed in some solvent which has preferentially removed the ink used to print the date, prefixes and bank title without causing similar damage to the remainder of the note. Date, prefixes and bank title were all printed together after the main printing of the note.

This note has been recorded in PSS, and was sold in Whytes, Dublin back in May 2017.
£1 note number 43NA 008483, was VG grade before its mutilation.

This is one of the more seriously washed notes I have seen anywhere. The seller is showing either an unusual degree of stupidity in not noticing the degree of destruction on the note, or bold-faced arrogance in offering it at £175 with the following comment "This Note May Have Been Pressed ~ I AM NOT SURE" and thinking that someone is going to buy it.

Whilst it is annoying to see morons destroying valuable and collectible notes, it is amusing to consider the horror of the person who washed the note in some solvent which dissolved parts of it, reducing a decent VG grade to a mutilated note worth around face value.

There are a lot of cretins out there. The trick is to not be one of them.

That £10 in the link looks ok to me. It's just a bad picture, overexposed with highlights blown.

Series B notes wrote:Reminds me: If the cleaning of a note doesn't mutilate it or dissolve ink, how is the note's value lowered?

Cleaning damages banknotes in various ways.
Certain detergents may not be fully washed out. Some harsher cleaning agents, bleach for example can damage the paper structure and lead to further damage down the line. Ironing melts the ink on the surface of the note. Immersion in a liquid removes the sizing (a protective coating on the surface which gives a note a nice glossy look and feel). The act of cleaning a note also damages the surface of the paper-sometimes you will see notes with fibres and threads sticking out, caused by abrasion.
Also, when a wet note drys out the inked and non-inked areas of paper are apt to dry at different rates, causing a rippling effect which is permanent.

A collector's banknote should be natural, as issued and used, and not messed with by others. Cleaning is done in an attempt to disguise the banknote's true appearance and grade, is thus dishonest.

Also, and importantly, dealers will offer a lower price when buying notes if they are cleaned, or simply refuse to buy them at all.